Additive for reducing viscosity in heavy crude oil

ABSTRACT

A method for increasing mobility of a heavy crude oil includes mixing an additive containing saponins and fatty acids with a heavy crude oil, wherein the saponins are derived from  Sapindus Saponaria.

BACKGROUND OF THE INVENTION

The invention relates to reduction of viscosity of heavy crude oils and, more particularly, to an additive and method for preparing the additive which help reduce viscosity in heavy crude oil.

Biodegradation of crude oil decreases crude oil quality and economic value. The resulting enrichment of heavy polar components leads to an increase in specific gravity, viscosity, (10,000 cps), acidity and content of sulfurs, asphaltenes and vanadium/nickel metals. These properties make it difficult to transport the extra heavy crude oil by pipeline.

Transportation of extra heavy oil outside of the well typically requires that the crude oil be heated or blended with diluents (BTX, light oils and kerosene) to reduce viscosity, or that the oil be upgraded on site, prior to transportation. Hence, decreasing the viscosity of the extra heavy crude oil decreases the amount of pumping energy required and potentially improves the transit time and productivity of the overall process. Technologies known to be used for reduction of viscosity of extra heavy crude oil include the use of inhibitors, solvent dilution, cracking, thermal fitting and preparation of emulsions.

Hayes et al. (U.S. Pat. No. 4,618,348) have disclosed bioemulsifier stabilized hydrocarbasols and their utilization and combustion of viscous hydrocarbons. This technology includes methods and compositions to facilitate the transportation and combustion of highly viscous hydrocarbons by forming reduced viscosity hydrocarbon in water emulsions, and in particular, bioemulsifier stabilized hydrocarbon in water emulsions.

Despite the above known efforts to address the undesirable viscosity of extra heavy crude oils, the need remains for improved methods and additives for reducing viscosity in heavy crude oils. The goal of the present invention is to address this need.

SUMMARY OF THE INVENTION

In accordance with the present invention, the foregoing goal has been attained.

Technical opportunities for advancement in reduction of viscosity of heavy crude oil include mechanical systems and saponins/fatty acids in systems which are dispersed through the oil without creation of water/oil emulsions. In accordance with the present invention, dispersal of a saponins/fatty acids system through heavy and extra heavy crude oils has been found to significantly reduce the viscosity of the extra heavy crude oil. The application of a natural-surfactant type biomarker for enhancing the flow characteristics of extra heavy crude oils is the result.

Heavy crude oils and extra heavy crude oil obtained from treatment with saponins/fatty acids in accordance with the present invention exhibits a lower mixing energy, is not emulsified, and has a lower operating cost and less environmental impact when compared with heavy and extra heavy crude oils which have been treated with synthetic surfactants and diluents.

In further accordance with the present invention, the saponins are preferably obtained from Sapindus Saponaria. The saponins obtained from a Sapindus Saponaria tree can advantageously be employed to convert viscous extra heavy crude oil into relatively low viscosity crude oil. The viscosity of the extra-heavy crude oil is reduced by 5-10 times through the addition of 0.5 to 10% wt. of saponins into the crude oil. This confirms the potential of saponins to produce crude oil having lower viscosity, and further confirms the marked activity of such saponins in lowering surface tension which facilitates long distance transportation of extra heavy crude oils.

Thus, in accordance with the present invention a method is provided for increasing mobility of a heavy crude oil comprising the steps of mixing an additive containing saponins and fatty acids with a heavy crude oil, wherein the saponins are derived from Sapindus Saponaria.

A typical heavy or extra heavy crude oil to be treated in this fashion may have a starting API gravity of <20° and a viscosity of greater than 10³ cP at 25° C. The crude may also have high content of sulfur, salts and metals such as nickel and vanadium. By treatment with the additive of the present invention, this viscosity can be improved into a range which allows efficient transportation.

Other objects and advantages of the present invention will appear hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of preferred embodiments follows, with reference to the attached drawings, wherein:

FIG. 1 is an illustration of the components of parapara tree (Sapindus saponaria) fruit pods.

FIG. 2 a shows an image of an extra heavy crude oil without the additive of the present invention and shows signs of very high surface tension;

FIG. 2 b shows an extra heavy crude oil with a saponin additive in accordance with the present invention, and very small air bubbles are shown which is indicative of low surface tension;

FIGS. 3 and 4 illustrate the FT-IR spectra of an extra heavy crude oil without additive and with additive in accordance with the present invention, respectively;

FIGS. 5 and 6 illustrate behavior of the viscosity of extra heavy crude oil without and with saponins and fatty acids in accordance with the present invention; and

FIG. 7 illustrates the viscosity behavior of an extra heavy crude oil treated in accordance with the present invention at different temperatures.

DETAILED DESCRIPTION

The invention relates to a method for increasing the mobility of a heavy crude oil, preferably through decreasing the viscosity of the heavy crude oil, through the use of an additive containing saponins which are derived from parapara fruit pods (Sapindus saponaria).

As described above, there is a need for more effective methods for reducing viscosity and improving the flowability of heavy and extra heavy crude oils. These crude oils are available in abundant supply, but their processing, refining and upgrading frequently require them to be transported over potentially long distances to facilities for conducting such processes.

Heavy and extra heavy crude oils can become more viscous and less flowable, due to biodegradation and migration, and this further increases the problems with transporting such crude oils.

In accordance with the present invention, it has been found that extract from the fruit pods of Sapindus Saponaria can be mixed with paraffins and olefins and added to the heavy and extra heavy crude oils. The mixing causes a dispersion of the additive through the crude oil, without forming an emulsion, but nevertheless impacts the wettability of the heavy and extra heavy crude oils and decreases viscosity as desired.

Suitable crude oils which can be treated with the additive according to the invention include heavy and extra heavy crude oils having a viscosity of at least about 10³ cP at 25° C. and an API gravity of less than 20°.

The additive for use in accordance with the present invention is preferably a mixture of saponins and fatty acids, and the different components of this additive are described herein.

The saponins are preferably obtained from Sapindus Saponaria, which is a native tree widely distributed throughout Venezuela. Venezuela has a large supply of heavy and extra heavy crude oils which would greatly benefit from the improvement in viscosity and the inventors have found that the saponins which can be obtained in significant quantities from the native tree are well-suited toward the improvement of viscosity.

The saponins which are desired are biomark, hopane type structures, such as steranes, and pentacyclic triterpenes. The saponins can be obtained from the fruit pods of Sapindus Saponaria. The pericarp of the fruit is extracted, and saponins can then be extracted from the pericarp.

The saponins of interest are glycosidic natural plant products, composed of a glycone to which is attached one or more glycosidic chains. Saponins are high molecular weight glycosides, consisting of a sugar moiety linked to a triterpene or steroid aglycone. The most common sources of saponins are the higher plants. Common names include: Parapara, Jaboncillo, soapberry and soapnut. The fruit, is a small leathery-skinned drupe having a 1-2 cm diameter, yellow ripening to blackish, containing one seed. The fruit is collected from eastern Venezuela. FIG. 1 illustrates the fruit, and shows pericarp and seed.

The saponins obtained in this manner are non-ionic natural surfactants based upon the chemical nature of the sapogenins as triterpenoidal and steroidal saponins. The saponins have a particle size which is relatively small in comparison with the structures of the asphaltenes and resins in the heavy and extra heavy crude oils, and the amphiphilic nature of the particles allows diffusion of the molecules, penetrating deeply and rapidly into the micellar agglomerates of the asphaltene-resins, allowing interaction with the electrons of the p orbital of the poly aromatic hydrocarbons in the matrix of the oil, and this has a stabilizing effect.

In order to prepare saponins according to the invention, the pericarp can be physically separated from the seed, and then finely cut with an electric cutter blade. The pericarp is placed in an extractor such as a Soxhlet extractor and crude saponins can be extracted with absolute ethanol. The ethanolic extract contains crude saponin or unpurified saponin. The ethanolic extract can be evaporated under reduced pressure and crude saponin is obtained. Another way to obtain the crude saponin is by simple extraction with ethanol at room temperature and pressure; but more time is needed to evaporate. Size exclusion chromatography can be used to separate saponins by size and molecular weights of the petroleum sample containing previously added saponins.

In accordance with the invention, the saponins are mixed with fatty acids such as a mixture of paraffins and olefins in order to prepare the additive of the present invention. Vegetable oils in particular are natural products of plant origin consisting of ester mixtures derived from glycerol with chains of fatty acid containing about 14 to 20 carbon atoms with different degrees of unsaturation. One important parameter of different vegetable oils is the amount of unsaturation of the constituent fatty acids. Unsaturated fatty acids are those that provide the affinity to mix petroleum and saponins, such as: Palm fatty acid distillate with oleic acid (35-37%) and linoleic acid (9-10%) or other vegetable oils with fatty acids, monounsaturated and polyunsaturated.

In accordance with the invention, the additive is formed by mixing the saponins and fatty acid in accordance with the present invention.

The heavy oil or extraheavy oil is heated to 60 ° C. with gentle agitation. Then, the unsaturated fatty acid is added, the mixture is homogenized and then added to 2% w/w of saponin extract is added. The percentages of the components in the mixture are:

-   -   Fatty acids, unsaturated and polyunsaturated 15-30% w/w     -   Saponins 2% w/w

Once the additive is formed, it can be mixed with the heavy or extra heavy crude oil, preferably at a concentration of between about 0.5 and about 10% weight of additive based upon weight of the crude oil being treated.

It is believed that the additive decreases viscosity through the fatty acid dispersing from the cells of asphaltenes and resins and being absorbed in the interface, and the polar interaction remains and is stabilized by the saponins. In equilibrium, the system (crude oil/natural surfactants) relaxes and flows easily.

The solubility of saponins/fatty acids, particle size and polar fractions in the extra heavy crude oil play a major role in viscosity reduction. Components of a crude oil were analyzed in an SARA analysis which determines content of Saturate, Aromatic, Resin and Asphaltene in crude oil, for a crude oil, and also a crude oil after treatment in accordance with the present invention. Table 1 below sets forth results of this comparison.

TABLE 1 SATU- ARO- SAMPLE RATED % MATICS % RESINS % ASPHALTENES % CRUDE OIL 15.80 36.20 37.96 10.03 CRUDE OIL 11.56 29.18 50.73  8.53 WITH SAPONINS

The results shown in Table 1 suggest the predominance of triterpenoid type structures (Hopane group) in the parapara saponins used in accordance with the present invention. The performance of the saponins from parapara as a natural surfactant and dispersement, without any modification, was evaluated using dispersion tests. The results are shown in FIGS. 2 a and 2 b, where FIG. 2 a shows a high surface tension extra heavy crude oil prior to treatment with the additive in accordance with the present invention, and FIG. 2 b shows much smaller bubbles indicating low surface tension in a crude oil which has been treated with an additive in accordance with the present invention.

The FTIR spectral characteristics of an extra heavy crude oil with and without the saponin additive in accordance with the present invention was also taken, and results of this analysis are shown in FIGS. 3 and 4. In these figures, the portion circled and indicated by the letter (a) show bands at 2950 cm⁻¹, 2921 cm⁻¹, and 2856 cm⁻¹, respectively, which are due to aromatic and aliphatic C—H stretching. The portion of these figures illustrated by circle (b) show bands at 1078 cm⁻¹, 1634 cm⁻¹, 1601 cm⁻¹, and 1454 cm⁻¹ and 1377 cm⁻¹ respectively corresponding to the aromatic C—C-stretching, asymmetric flexion of the aliphatic C—H, symmetric flexion of the aliphatic C—H, and stretching of O—H and C═O at 3428 and 1708 cm⁻¹, respectively. The key difference between the two spectra shown in FIGS. 2 and 3 is the higher intensity of the O—H and C═O (a*/b*) bands at 2921 and 1708 cm⁻¹. This is due to the presence of the —OH groups (triterpenes of the saponins) and carboxylic groups of the fatty acids and saponins.

The additive in accordance with the present invention was further evaluated through comparison of behavior of viscosity of extra heavy crude oil without additive (FIG. 5) and the behavior of the same extra heavy crude oil with additive (FIG. 6). These measurements were taken at different temperatures and show the viscosity over increasing shear rates. As shown, viscosity is very high for the un-treated extra heavy crude oil, at a temperature of 40° C., and significant shear rate is required in order to reduce the viscosity to a suitable level. Heating the crude oil to temperatures of 50° C. and 60° C. also reduces the viscosity, but the level is still very high.

FIG. 6 shows the viscosity of the same extra heavy crude oil in accordance with the present invention, and shows significant improvement in viscosity at all comparable temperatures. Thus, using the additive of the present invention, the extra heavy crude oil evaluated would be much more easily flowable at a temperature of 40° C. for example, as compared to the untreated extra heavy crude oil.

FIG. 7 shows an analysis of viscosity behavior of an extra heavy crude oil without any additive, and with a fatty acid and saponin additive in accordance with the present invention. The results illustrated in FIG. 7 show viscosity behavior of the tested samples at different temperatures, and the best results are shown with the additive in accordance with the present invention. The graph of the natural logarithm of viscosity (lη) versus the reciprocal temperature in degrees kelvin (1/T, K), is a way to represent the relationship between viscosity and temperature, to highlight more clearly the orders of magnitude of the viscosity variable and appreciate better than additive is more efficient.

It should be readily appreciated that the method and additive in accordance with the present invention advantageously allows for significant reduction in viscosity of heavy and extra heavy crude oils as desired in accordance with the present invention. This can reduce the cost for transportation of the heavy and extra heavy crude oils allowing such potentially valuable crude oils to be transported as needed. Further, the additive used to make this improvement in viscosity is environmentally friendly and it is derived from a locally readily available source.

One or more embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A method for increasing mobility of a heavy crude oil, comprising mixing an additive containing saponins and fatty acids with a heavy crude oil, wherein the saponins are derived from Sapindus Saponaria.
 2. The method of claim 1, further comprising the step of obtaining the saponins from Sapindus Saponaria.
 3. The method of claim 1, wherein the saponins are derived from pericarp of the fruit pods of Sapindus Saponaria.
 4. The method of claim 1, wherein the saponins are derived by extracting with an organic solvent.
 5. The method of claim 1, wherein the saponins are selected from the group consisting of triterpenoids and corresponding 2-β-methyl derivatives with C₂₃, C₂₄, C₂₈, C₂₉ and C₃₀, hexones and furanose.
 6. The method of claim 1, wherein the fatty acids are selected from the group consisting of saturated, unsaturated and polysaturated fatty acids linked to other chemical functional groups.
 7. The method of claim 1, wherein the additive is mixed with the heavy hydrocarbon such that the saponins are present in an amount between 0.01 wt. % and 30 wt. % based on weight of the hydrocarbon.
 8. The method of claim 1, wherein the mixing step forms a single phase dispersion of the additive through the heavy crude oil.
 9. The method of claim 8, wherein the single phase dispersion has reduced viscosity as compared to the starting heavy crude oil. 